My advice--the best way to improve the quality of your shots is to learn how to use off-camera lighting effectively.Of course, I'mone of this forum's biggest strobist advocaters--so I might be a bit biased.


The following was taken with 3 off-camera flashes (all 285HVs if I remember correctly) using the 70-200 f/2.8 L IS. However, I shot it at f/4, 1/200 sec, ISO 100, so it would be perfectly doable with the 70-200 f/4.
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My off-camera lighting kit has grown substantially over the past 2 years, and I'm nowhere near done buying equipment. But, I always try totake the best pictures I can with the gear that I have, and buy more whenever I think it's necessary (or else just to try something new).


Start off with a strobe, a lightstand, a swivel, an umbrella, and a triggering system. Once you start getting the hang of it, then buy more as needed. Save some money by making your own light modifiers like snoots and grids.